Studies are proposed which aim to understand the biology of the pancreatic allograft. Inbred strains of rats will receive either a duct-ligated or duct-open pancreatic allograft and the effect of differing histocompatibility, active and passive enhancement and non-specific immunosuppression on allograft function and survival will be evaluated. In addition, the susceptibility of whole pancreas grafts to humoral immunity in bone marrow and lymph node tolerant rats will be compared to that of isolated pancreatic islets of Langerhans. A model of an immediately vascularized fetal pancreas will also be evaluated to determine whether the whole organ is more or less vulnerable to the rejection reaction than isolated islets in the same histocompatibility combination.